Marlène Palluel

Bio: Marlène Palluel is an academic researcher from University of Bordeaux. The author has contributed to research in topics: Spin crossover & Surface plasmon resonance. The author has an hindex of 1, co-authored 3 publications receiving 11 citations.

The Interplay between Surface Plasmon Resonance and Switching Properties in Gold@Spin Crossover Nanocomposites

Abstract: Rod-like gold nanoparticles are directly embedded in a 1D-polymeric spin crossover (SCO) material leading to singular Au@SCO nanohybrid architectures. The resulting architectures are designed to promote a synergetic effect between ultrafast spin-state photoswitching and photothermal properties of plasmonic nanoparticles. This synergy is evidenced by the strong modulation of the surface plasmon resonance of the gold nanorods through the spin-state switching of the SCO component and also the strong enhancement of the photoswitching efficiency compared to pure SCO particles. This remarkable synergy results from the large modulation of the dielectric properties of the SCO polymer upon its thermal switching and the enhancement of the heating of these hybrid nanostructures upon excitation of the surface plasmon resonance of the gold nanorods.

Photo-Thermal Switching of Individual Plasmonically Activated Spin Crossover Nanoparticle Imaged by Ultrafast Transmission Electron Microscopy.

Abstract: Spin Crossover (SCO) is a promising switching phenomenon when implemented in electronic devices as molecules, thin films or nanoparticles. Among the properties modulated along this phenomenon, optically induced mechanical changes are of tremendous importance as they can work as fast light-induced mechanical switches or allow to investigate and control microstructural strains and fatigability. The development of characterization techniques probing 2 nanoscopic behaviour with high spatio-temporal resolution allows to trigger and visualize such mechanical changes of individual nanoscopic objects. Here we use Ultrafast Transmission Electron Microscopy (UTEM) to precisely probe the length changes of individual switchable nanoparticles induced thermally by nanosecond laser pulses. This allows us to reveal the mechanisms of spin switching, leading to the macroscopic expansion of SCO materials. This study was conducted on individual pure SCO nanoparticles and SCO nanoparticles encapsulating gold nanorods that serve for plasmonic heating under laser pulses. Length changes are compared with time-resolved optical measurements performed on an assembly of these particles.

Rational direct synthesis of [Fe(Htrz)2(trz)](BF4) polymorphs: temperature and concentration effects

Abstract: The [Fe(Htrz)2trz](BF4) compound is probably the most studied in the spin crossover (SCO) community since it exhibits switching properties with a large temperature range of memory effect, just above room temperature. We present in this paper a detailed study of the influence of the synthetic parameters on the polymorphism of this compound. While the crystal structure of polymorph I is already known, we report the crystal structure of polymorph II and discuss the differences to allow further studies to discriminate between the two. This was achieved through the resolution of the crystal structure of the [Fe(Htrz)2(trz)](PF6) analogue. This study allows us to draw a phase diagram and to discuss the effect of the reaction conditions on the formation of polymorphs, the size of the particles and their properties.

Laser-Driven Transient Phase Oscillations in Individual Spin Crossover Particles.

Abstract: An unusual expansion dynamics of individual spin crossover nanoparticles is studied by ultrafast transmission electron microscopy. After exposure to nanosecond laser pulses, the particles exhibit considerable length oscillations during and after their expansion. The vibration period of 50-100 ns is of the same order of magnitude as the time that the particles need for a transition from the low-spin to the high-spin state. The observations are explained in Monte Carlo calculations using a model where elastic and thermal coupling between the molecules within a crystalline spin crossover particle govern the phase transition between the two spin states. The experimentally observed length oscillations are in agreement with the calculations, and it is shown that the system undergoes repeated transitions between the two spin states until relaxation in the high-spin state occurs due to energy dissipation. Spin crossover particles are therefore a unique system where a resonant transition between two phases occurs in a phase transformation of first order.

Iconography : Molecular electronics: Scanning tunneling microscopy and single-molecule devices

Abstract: Comptes Rendus Chimie - In Press.Proof corrected by the author Available online since jeudi 19 juillet 2018

Imaging the Thermal Hysteresis of Single Spin-Crossover Nanoparticles.

Abstract: The magnetic hysteresis property during the spin transition of spin-crossover (SCO) materials holds great promise for their applications in spin electronics, information storage, thermochromic, and nanophotonic devices. Existing studies often measured the averaged property of a bulk sample consisting of lots of individuals. When considering the significant heterogeneity among different individuals and the inevitable interparticle interactions, ensemble measurement not only blurred the structure-property relationship but also compromised the intrinsic hysteresis property and cyclability. Herein, we employed a recently developed surface plasmon resonance microscopy (SPRM) method to measure the thermal hysteresis curve of single isolated SCO nanoparticles. The thermal-induced spin transition was found to alter the optical contrast of single SCO nanoparticles, which was optically readout using SPRM in a quantitative, nonintrusive, and high-throughput manner. Single nanoparticle measurements revealed an intrinsic transition temperature that was independent of the temperature scan rate and superior stability after over 11 000 cycles of single SCO nanoparticles. Correlations between the hysteresis and the size and morphology of the same individuals further uncovered the significant nanoparticle-to-nanoparticle heterogeneity with implications for the size-property relationship and rational design of SCO materials with improved performance.

Room temperature optoelectronic devices operating with spin crossover nanoparticles.

Abstract: Molecular systems can exhibit multi-stimuli switching of their properties, with spin crossover materials having unique magnetic transition triggered by temperature and light, among others. Light-induced room temperature operation is however elusive, as optical changes between metastable spin states require cryogenic temperatures. Furthermore, electrical detection is hampered by the intrinsic low conductivity properties of these materials. We show here how a graphene underlayer reveals the light-induced heating that triggers a spin transition, paving the way for using these molecules for room temperature optoelectronic applications.

Plasmon-assisted spin transition in gold nanostar@spin crossover heterostructures

Abstract: Herein we report the design of core@shell nanoparticles formed by a metallic Au nanostar core and a spin-crossover shell based on the coordination polymer [Fe(Htrz)2(trz)](BF4). This procedure is general and has been extended to other metallic morphologies (nanorods, nanotriangles). Thanks to the photothermal effect arising from the plasmonic properties of the Au nanostar, 60% of iron centers undergo a thermal spin transition inside the thermal hysteresis triggered by a 808 nm laser low intensity irradiation. Compared to other Au morphologies, the great advantage of the nanostar shape arises from the hot spots created at the branches of the nanostar. These hot spots give rise to large NIR absorptions, making them ideal nanostructures for efficiently converting light into heat using low energy light, like that provided by a 808 nm laser.

Bistable spin-crossover in a new series of [Fe(BPP-R)2]2+ (BPP = 2,6-bis(pyrazol-1-yl)pyridine; R = CN) complexes.

Abstract: Spin-crossover (SCO) active transition metal complexes are a class of switchable molecular materials. Such complexes undergo hysteretic high-spin (HS) to low-spin (LS) transition, and vice versa, rendering them suitable for the development of molecule-based switching and memory elements. Therefore, the search for SCO complexes undergoing abrupt and hysteretic SCO, that is, bistable SCO, is actively carried out by the molecular magnetism community. In this study, we report the bistable SCO characteristics associated with a new series of iron(ii) complexes-[Fe(BPP-CN)2](X)2, X = BF4 (1a-d) or ClO4 (2)-belonging to the [Fe(BPP-R)2]2+ (BPP = 2,6-bis(pyrazol-1-yl)pyridine) family of complexes. Among the complexes, the lattice solvent-free complex 2 showed a stable and complete SCO (T1/2 = 241 K) with a thermal hysteresis width (ΔT) of 28 K-the widest ΔT reported so far for a [Fe(BPP-R)2](X)2 family of complexes, showing abrupt SCO. The reproducible and bistable SCO shown by the relatively simple [Fe(BPP-CN)2](X)2 series of molecular complexes is encouraging to pursue [Fe(BPP-R)2]2+ systems for the realization of technologically relevant SCO complexes.